To write properly on an optical disc a laser is controlled with a certain pattern, a so-called write strategy. Mostly, but not always, write strategies are stored on the disc with write strategy parameters, for instance as information stored in a modulated wobble for DVD recordable and rewritable discs and for BD recordable and rewritable discs (BD-R and BD-RE respectively). But this information is not always the correct or the optimum write strategy because the write strategy tuned by the disc manufacturer is generally done on a certain reference drive. The optical path of these reference drives is different compared with practical optical drives. The write strategy stored on the disc is thus not the optimal one for use in a practical optical disc drive, and depending on the system margins of the practical disc drive it is possible that certain discs on a certain speed are not written properly when used with the write strategy information as retrieved from the disc.
WO2006097873A2 describes an apparatus and a corresponding method for determining write strategy parameters for recording data on an optical record carrier. The apparatus is proposed in WO2006097873A2 comprises:
initialization means for setting initial write strategy parameters,
setting means for setting initial variable levels and an initial experimental plan, based on variations of said initial write strategy parameters, for use in a design of experiments method for optimization of said write strategy parameters,
optimization means for determining optimized write strategy parameters by use of a design of experiments method, and
iteration means for checking if, based on a predetermined criterion, the optimized write strategy parameters determined by the optimization means shall be further optimized and, in case the write strategy parameters shall be further optimized, for determining new variable levels and a new experimental plan for use in another iteration of the design of experiments method for further optimization of said write strategy parameters.
The optimization means of WO2006097873A2 may comprise:
test recording means for performing test recordings on said record carrier a predetermined number of times using variations of said initial write strategy parameters as set in the variable levels and the experimental plan used by the design of experiments method,
measurement means for measuring a quality parameter value of a quality parameter for each test recording indicating the recording quality of said test recording, and
determination means for determining optimized write strategy parameters by evaluation of the measured quality parameter values for said test recordings.
The determination means WO2006097873A2 may be adapted for determining the optimized parameters by use of a model, in particular a second-order model, and by determining an optimum, in particular a minimum, of said model.
The method described in WO2006097873A2 may work well when the write strategy has a relatively limited number of parameters. However, many standard write strategies associated with optical disk standard comprise a large number of independent parameters in the description of the standard write strategy as standardized. Especially for high-density recording systems using blue lasers to achieve a small spot size on the optical disk, the number of write strategy parameters is large. For example, in the BD-R and BD-RE standard, the number of write strategy parameters is large, e.g., 34 (4 power levels and 30 timing parameters) for a BD-R castle type write strategy and 49 (4 power levels and 45 timing parameters) for a BD-RE N−1 pulsed type write strategy, and their values need to be accurately applied. This may cause the method of WO2006097873A2 for determining write strategy parameters to take a larger amount of time than is acceptable.
Moreover, the high-density recording systems with blue lasers, like BD-R and BD-RE, and also HD-DVD systems, require a even more precisely controlled write strategy than the earlier lower-density red laser-based DVD systems. In effect, convergence to precise and robust write strategy parameters may be hampered when using the method of WO2006097873A2 without any further measure.
Also the use of a second-order model for determining optimized parameters as described in WO2006097873A2 may fail or result in a erroneous results, e.g., due to a mis-convergence, when used without any further measure.